This invention relates to media which can be imaged by exposure to actinic radiation. More particularly, the invention relates to articles capable of being used for imaging based on photochromic aziridines, which allow the image-forming operation to be reversible, i.e., the recorded image may be erased.
Many conventional imaging materials undergo irreversible changes when exposed to actinic radiation. Thus, erasure is impossible without physical destruction of the image itself. Additionally, in many instances, the image formed is latent, and subsequent development is necessary.
Photochromes are compounds which change color reversibly on exposure to actinic radiation. Such direct-developing photochromic materials, however, traditionally suffer the limitation that images produced from systems containing these materials have very little stability, i.e., the image will fade spontaneously within a few minutes or hours at room temperature.
It has now been ascertained that particularly defined photochromic aziridine compounds can be utilized for imaging wherein the recorded image may be erased and information may be added, the film may be re-used, etc.
In Schleigh et al, U.S. Pat. No. 3,894,874, there is described the use of aziridines in photoreductive imaging. A reducible, image-forming compound is combined with the photochromic aziridine in a binder on a substrate to form a radiation-sensitive layer. Upon exposure to actinic radiation, followed by heating, an image may be obtained. Furthermore, partly crystalline and partly crystallographically aligned photochromic aziridines and oxiranes are disclosed as having utility in windshields, sunglasses, and light switching devices in U.S. Pat. No. 3,964,823.
It has now been found that by applying hereinafter-defined photochromic microcrystalline aziridines onto a substrate, and by utilizing an oxygen barrier material to cover the microcrystalline aziridine coating, or by incorporating same in the coating application solution, the lifetime of the image formed by exposure to actinic radiation can be increased at least a thousand times more than that of the photochromic aziridine in oxygen or air.